1. The Field of the Invention
This invention relates to standardizing interfaces of computer equipment in a network structure. More particularly, this invention relates to implementing a standardized interface compatible with a plurality of interfaces common to Integrated Services Digital Networks (ISDN).
2. Present State of the Art
Increasingly, users of personal computers and related computer equipment employ and utilize public and private telephone lines to transmit and receive data. Such a capability of interconnecting a computer with a plurality of locations dramatically increases the value of a computer and the productivity of the computer user. As the number of accessible public and private networks increases so also does the public's use of such systems. As is well-known, computer equipment such as personal computers, communicate across telephone lines, such as the Public Switched Telephone Network (PSTN) and interact with remote sites using the existing infrastructure of the PSTN. Traditional interfacing of a personal computer with the PSTN has occurred through the use of modem technology. The term "modem" is an acronym derived from the phrase "modulator-demodulator," which is descriptive of the basic function performed by the modem. A modem permits the personal computer, which is a digital device, to be interfaced with telephone lines by modulating the outgoing digital data into a form compatible with the telephone network, which is designed to handle analog signals. Similarly, the modem reverses that process by demodulating incoming analog data from the telephone lines so that it is in a digital form that is usable by the computer.
The manner in which telephone equipment is interfaced to a public or private telephone network, both physically and electrically, has been largely standardized. That is to say, a personal computer user having a modem may confidently compatibly interconnect with the PSTN using a standard telephone cable. One of the standardized interfacing components of the PSTN system is the physical media connector through which telephone equipment may be physically and electrically connected to the telephone subscriber line. The standard media connector used in the United States is the RJ-11, six pin miniature module and plug. As is well-known, most telephone equipment is equipped with the RJ-11 module, into which is received the RJ-11 plug and associated twisted-pair telephone cable, which is then plugged into, for instance, a telephone wall jack, also a standard RJ-11 module. In this manner, the telephone, modem, or other related telephone equipment is physically and electrically interfaced with the telephone subscriber loop. Voice or transmission data is then transmitted in analog form through the RJ-11 physical/electrical media connector into the telephone line.
As additional users utilize the network created by the PSTN, and as individual users demand enhanced bandwidth for multimedia information, standard PSTN data transmission rates are strained and often inadequate. To facilitate the transmission of larger amounts of data across a network, additional network standards have evolved. For example, Integrated Services Digital Network (ISDN) provides an improved partitioning of the physical network resources into channels. A typical standard ISDN service provides two B-channels operating at a combined frequency of 128 Kbps and one D-channel for exchanging digital data at much higher rates than standard PSTN analog systems. Such an ISDN standard has become universally accepted throughout the world as a higher data rate system while ISDN compatible equipment has also become commonplace.
Although the ISDN system standards have become internationally accepted, implementations and configurations associated with interfacing two ISDN systems have not become standardized. For example, the ISDN system is comprised of a series of "reference points" which define physical interfacing locations. Referring to FIG. 1, reference points that are in common use for ISDN systems include the R, S, T and U reference points. It is not uncommon to refer to the S and T reference points in combination as S/T or just as the S with an implied T reference point.
Referring to FIG. 1, a U reference point 24 provides the access interface point for ISDN 26. U reference point 24 provides the physical interface point through which the wiring routes directly to the local network service provider. Such an interface corresponds to a connection jack located within a commercial or residential installation. In the United States, U reference point 24 represents the termination of the services provided by the network provider such as a telephone company. Other additional interfaces and equipment are implemented within user equipment attached thereto. In ISDN implementations outside of the United States, an S reference point 16 or a T reference point 20, also commonly known as the S/T reference point, is included in the physical service or equipment provided by the network service provider to a user. Such a difference between national and international standards becomes extremely important for utilization of non-domestic equipment and utilization of existing ISDN configurations by world travelers. That is to say, users of a personal computer 10 and associated equipment such as a terminal adaptor 14 in the United States must employ a special device to handle the physical interface translation through an NT-1 equipment 22. While some equipment incorporates the U reference point to S/T reference point translation, other equipment requires a separate NT-1 22 equipment for signal translation. For completeness, an R reference point 12 denotes the point between an ISDN terminal adaptor 14 and non-ISDN equipment such as personal computer 10.
Due to the global discrepancies in the reference point provided to a user for interfacing their communication equipment, substantial confusion and damage may result from inadvertent interconnection with an incompatible interface. Such differences in interface standards provided by service providers require an unnecessary level of sophistication on the part of the user to identify which reference point is being provided by the service provider. Further confusion is induced due to the commonality of accepted physical interface standards. For example, both the U reference point and the S/T reference points employ a standard RJ-45 connector as the standardized interfacing telephone receptacle. However, as introduced above, the electrical standards for the U reference point and the S/T reference point differ considerably. For example, the U reference point provides a DC voltage of 52 volts between pins 4 and 5 on the RJ-45 connector. Although the RJ-45 connector is a six pin connector, the U interface is standardized as a 2-wire interface utilizing only pins 4 and 5. The S/T reference, on the other hand, also utilizes the RJ-45 connector, however, the S/T reference point employs a 1.25 volt peak-to-peak clock running at 97 kHz on the receive differential pair. The 97 kHz clock of the S/T reference point is also carried on pins 4 and 5 of the RJ-45 connector.
Prior configurations of equipments for interfacing with an ISDN system have provided both the U reference point interface in one connector while providing a separate distinct connector compatible with the S/T reference point. Such a dual configuration required a user to select the compatible reference point for equipment connection with the service provided by the service provider.
Thus, it appears that there exists no present technique for providing a common interface from which a user of communication equipment may interface directly with an ISDN system regardless of the reference point provided by the ISDN service provider. Furthermore, there does not currently exist a technique for automatically sensing and adapting a common interface on ISDN equipment with an unknown reference point supported and provided by an ISDN service provider. Therefore, a need exists for providing a method and system for automatically configuring an ISDN equipment interface for compatible operation with either a U reference point as provided by a portion of ISDN service providers or an S/T reference point as provided by yet another portion of ISDN service providers, without requiring a user of the ISDN equipment to determine the nature of the reference point provided by the ISDN service provider.